An automobile has various auxiliaries driven by an engine, and one of these auxiliaries is an air conditioner compressor and an endless belt extends between a driven pulley provided on the end of the rotary shaft of the compressor and a driving pulley of the engine so that the compressor is operated. An example of such a compressor is shown in FIG. 4.
In a compressor 51 for vehicle compressor shown in FIG. 6, a piston 54 is disposed in a plurality of cylinders 53 formed in a casing 52 in such an arrangement that it can move back and forth, and a swash plate 56 is slidably clamped between semicircular shoes 55, 55 provided opposed to each other on the base of the piston so that the piston 54 moves back and forth when the swash plate 56 is rotated. Thus, in order to allow the piston 54 to smoothly slide in the cylinder 53 formed in the casing 52 and reduce the weight of the compressor 51, the casing is mostly made of an aluminum alloy such as high silicon material content aluminum alloy.
A pin 78 provided at the end of an arm 57 fixed to the swash plate 56 is fitted in an ellipsoidal hole 62 provided in a rotary driving member 61 which rotates integrally with the rotary shaft 60, and a sleeve 63 having a spherical surface is fitted on the rotary shaft 60 so that it is energized in the axial direction by a spring 59 and rotatably supports the swash plate 56 on the periphery thereof.
As in the compressor 51, there may be provided a variable volume pump comprising a pressure-sensitive member 49 which expands or shrinks according to the pressure in a suction chamber 64 to open or close valve so that the balance pressure against the back surface of the piston 54 is adjusted by the suction pressure of the compressor to allow the inclination angle of the swash plate 56 to change according to the balance pressure and hence adjust the stroke of the piston 54, keeping the suction pressure constant.
In the compressor 51 shown in FIG. 6, an electromagnetic clutch 65 is provided, a leaf spring 67 is fixed to a mounting bracket 66 provided on the end of the rotary shaft 60, and the leaf spring 67 has an annular plate 68 made of a magnetic material fixed to the peripheral forward end thereof. In the embodiment shown, a driven pulley 73 having a U-shaped section is supported on the periphery of a supporting axis portion 71 protruding from an end casing 70 of the compressor 51 via a bearing 72.
In the space having a U-shaped section is disposed a solenoid 74 fixed to the end casing 70, and the aforementioned annular plate 68 made of a magnetic material is disposed opposed to the solenoid 74 with an annular wall 75 of the driven pulley 73. Further, as the aforementioned bearing 72 there is normally used a bearing for vehicle compressor pulley having an outer diameter of 65 mm or less or optionally a bearing with seal having a grease enclosed therein.
As mentioned above, the casing 52 is made of an aluminum alloy, and the end casing 70 is similarly made of an aluminum alloy to reduce the weight thereof, and accordingly, the supporting axis 71 on which the inner ring 69 of the bearing 71 is fitted is made of an aluminum alloy.
In the electromagnetic clutch 65 shown in FIG. 6, when the solenoid 74 is not energized, the aforementioned annular plate 68 is positioned apart from the annular wall 75 of the driven pulley 73 as shown so that even when the driven pulley 73 is rotated by the endless belt, the annular plate 68 does not rotate and the compressor 51 does not operate accordingly. On the contrary, when the solenoid 74 is energized, the resulting magnetic force causes the solenoid 74 to attract the annular plate 68 made of a magnetic material so that the annular wall 75 is pressed against the annular wall 75 of the driven pulley 73. In this manner, the electromagnetic clutch 65 is in connected state so that when the driven pulley 73 rotates, the annular plate 68 rotates integrally therewith to rotate the swash plate 56 via the leaf spring 67, the mounting bracket 66 and the rotary shaft 60 as mentioned above, causing the piston 54 to move back and forth to operate the compressor 51.
As the bearing 72 which bears the driven pulley 73 for rotating the rotary shaft 60 of said compressor 51 rotatably relative to the casing there has been heretofore used any of various types of bearings, but a double-row angular bearing is often used to prevent the frequent imposition of unbalanced load on the driven pulley 73 by the belt resulting in the discrepancy and oblique disposition of the central axis of the inner ring 69 and the outer ring 79 of the bearing.
As mentioned above, in the bearing for automobile compressor pulley, the portion on which the inner ring is fitted is mostly an axis-shaped portion protruding from the casing of the compressor, and in the embodiment shown in FIG. 6, it is a supporting axis 71 protruding from the end casing 70. Accordingly, the supporting axis 71 is a part of the member constituting the casing and is therefore made of a light alloy such as aluminum alloy. Further, the portion in which the outer ring of the bearing is fitted is mostly a driven pulley which is made of iron. Moreover, the driven pulley is sometimes made of resin in recent years.
On the contrary, since the bearing is subject to great load developed when the compressor is driven and must rotatably bear the compressor in a stable manner over an extended period of time, it must be made of a bearing steel having a high strength and have its races properly surface-treated. Therefore, it is inevitable that the bearing and the member on which the inner ring and the outer ring of the bearing are fitted must be made of different materials.
In particular, while most light alloys such as aluminum alloy have a great linear expansion coefficient, the bearing steel has a relatively small linear expansion coefficient, and since the recent rise of the internal temperature of engine room and the temperature during bearing operation cause the rise of the ambient temperature of the bearing and hence the expansion of the range of the working temperature of the bearing, the difference in linear expansion coefficient between the two materials has given a great problem.
In other words, in the case where the compressor pulley is born by the casing of the compressor via a bearing, when the inner ring 69, for example, is fitted on the supporting axis 71 protruding from the end casing 70 with a conventional degree of interference, the supporting axis 71 expands greater than the inner ring 69 when the temperature is higher than expected, developing an extremely great force pressing against the interior of the inner ring. Therefore, the inner ring is deformed to increase its diameter, causing gradual decrease of initial clearance which is the bearing clearance predetermined at assembly and eventually rolling of balls compressed between the inner ring and the outer ring, i.e., negative value of so-called running clearance. Further, the negative value gradually increases with said temperature rise.
When the running clearance is negative as mentioned above, the races on the inner ring and the outer ring and the surface of the balls gradually undergo damage and short life due to fatigue and temperature rise accompanying prolonged operation and this is extremely undesirable. When the looseness of fitting of the shaft with the bearing is raised to cope with this problem, relative slippage occurs between the inner ring and the supporting axis to disable proper bearing action and generate noise at low temperature because the connecting force of the two parts is small.
Further, as a countermeasure for preventing the aforementioned running clearance from being negative, it can be proposed that the initial clearance of the bearing is predetermined greater in expectation of reduction of clearance. In this case, however, a great clearance occurs in the bearing during low temperature operation, causing the general formula of great noise, and this is undesirable.
On the other hand, for the outer ring 79 of the bearing, the driven pulley 73 in which the outer ring 79 is fitted is sometimes made of a material having a greater linear expansion coefficient than that of the outer ring, and in recent years, a pulley made of resin is sometimes used. Accordingly, when the expansion of the driven pulley becomes great particularly during high temperature operation, the interference of the outer ring which has been initially assembled to the driven pulley with a predetermined interference is gradually lost, causing slippage relative to each other. As a counter measure for coping with this problem, it can be proposed that the interference during the assembly of the driven pulley and the bearing is sufficiently raised, making it possible to sufficiently maintain the connecting force between the two parts and hence prevent the occurrence of slippage relative to each other even during high temperature operation.
However, when such a great interference is predetermined, a great external force is acted on the outer ring to deform the outer ring, and in a bearing which has been predetermined to a certain initial clearance, the outer ring is provided with a clearance decreased by the inward deformation, occasionally making the initial clearance negative and hence causing trouble during low temperature operation to disadvantage. Further, since the linear expansion coefficient of the material is great, an extreme negative clearance occurs at an extremely low temperature, causing problems such as excess torque and dent on the bearing race. Moreover, the rise of the initial clearance for the purpose of preventing this problem causes the rise of clearance at high temperature resulting in the generation of noise. This trouble is not limited to bearing for automobile compressor pulley but can apply to pulley bearings for other various engine auxiliaries.
Accordingly, a first object of the present invention is to provide a bearing for pulley of engine auxiliary which can prevent the excessive reduction of running clearance caused by the expansive deformation of the inner ring by the expansion of the mounting member side thereof at high temperature even if the linear expansion coefficient of the inner ring of the bearing and the member on which the inner ring is fitted differ greatly from each other, can prevent the generation of noise at low temperature when the initial clearance of the bearing is raised to cope with this problem, can prevent the occurrence of slippage of the outer ring relative to the mounting member due to the reduction of interference of the bearing caused by the increase of the inner diameter of the outer ring by the expansion on the mounting member side thereof a thigh temperature even if the linear expansion coefficient of the outer ring of the bearing and the member in which the outer ring is fitted differ greatly from each other and can prevent the excessive reduction of initial clearance caused by the shrinkage deformation of the outer ring developed when the interference has been previously raised to cope with the reduction of interference or by the shrinkage of the outer ring at extremely low temperature. Further, a second object of the present invention is to solve problems that occur when some means for solving said problems are employed and hence provide a more complete bearing for pulley of engine auxiliary.